As is well known, so-called horizontal-axis wind turbines are widely used in industry such as for wind-generated electricity. A horizontal-axis wind turbine comprises a rotor having one or more blades that are radially attached to a hub, a nacelle that is connected to the hub and supports the axle of the rotor via a main shaft that extends in the horizontal direction, and a tower that is erected in a vertical direction, supports the nacelle so that it has free yaw rotation.
Conventionally, variable pitch type horizontal-axis wind turbines that drive and control the pitch angle of the blades have been used. As a variable pitch type wind turbines there is the interlocked type in which the pitch angles of all of the blades are mechanically linked and controlled together by a link mechanism, as well as recently independent variable pitch type horizontal-axis wind turbines having a pitch drive control system for each blade that can independently control the pitch angle for each blade have been used. In an independent variable pitch type horizontal-axis wind turbine, it is possible to prevent over rotation of the rotor and maintain safety in strong wind by feathering one or more or all of the blades even when a pitch drive device for one of the blades is broken.
On the other hand, in regards to yaw control, a yaw drive control device that can freely control the drive of the yaw rotation of the nacelle and therefore the rotor, and a yaw brake that brakes the yaw rotation have conventionally been used in horizontal-axis wind turbines.
In patent document 1 (Japanese Unexamined Patent Application Publication No. 2005-30263) a pitch angle control device for the wind turbine blades is disclosed that, by providing a sub motor in addition to a main motor, is capable of maintaining safe operation of the wind turbine when the main motor or its control unit fails, even during strong winds, by operating the sub motor and rotating the wind turbine blades to the point of feathering.
However, even the conventional technology had the following problems.
In the pitch angle control device disclosed in patent document 1, part of the transmission mechanism for transmitting drive force to the blades is shared by both the main motor and sub motor. In other words, in FIG. 1 of patent document 1, a gear reducer, the output shaft thereof, and the external gear that is connected to the output shaft, and an internal gear that are provided for the blades and engages with the external gear are a transmission mechanism that is shared by the main motor and sub motor.
Therefore, when some kind of foreign matter gets caught in the section where the gears engage and the shared transmission mechanism becomes inoperable, pitch control become impossible, and both the main motor and sub motor become useless.
Even in the case where a sub motor system as disclosed in patent document 1 is applied to the yaw drive of the nacelle, the same problem occurs as long as there is a shared transmission mechanism.
In a sub motor system as disclosed in patent document 1, the use of the sub motor is limited to the feathering of the blades when the main motor fails and there is a strong wind, and thus, it is lacking in the applicability of having two motors.
Furthermore, there is another problem in that in the objects to be driven such as the blades or nacelle, or the ring gear that is fastened to the base section such as the hub or tower, not all of the gear teeth are equally used, so the teeth in a limited angular range quickly wear out, shortening the life of the gears.
Considering the problems with the conventional technology, the object of the present invention is to provide a horizontal-axis wind turbine comprising a dual pitch drive mechanism that is independent up to the transmission mechanism for one blade, or a dual yaw drive mechanism that is independent up to the transmission mechanism for one turbine nacelle, and provides new usability of a dual drive system.